1. Field of the Invention
The present invention relates to a magnetic recording medium comprising a nonmagnetic support and a magnetic recording layer.
2. Description of prior arts
A magnetic recording medium comprising a nonmagnetic support and a magnetic recording layer is used as an audio tape, a video tape, or a recording medium for a computer system. The magnetic recording medium basically comprises a nonmagnetic support of a resin film having a high strength such as a polyethlene terephthalate resin, and a magnetic recording layer provided on the support. The magnetic recording layer comprises a binder and a ferromagnetic powder dispersed therein.
As a binder material for the magnetic recording layer, there has been conventionally employed a material mainly containing a copolymer having a repeating unit consisting of vinyl chloride, vinyl acetate, and maleic anhydride (hereinafter referred to sometimes as "a vinyl chloride/vinyl acetate-type resin").
Recently, according to the improvement of a recording and reproducing device, etc., a magnetic recording medium at higher level in various properties as compared with a conventional one is desired, and hence a combination of a vinyl chloride/vinyl acetate-type resin and a polyurethane resin has been employed as a binder in place of the conventional binder material. The reason is that the vinyl chloride generally is so rigid as to show relatively poor contact with a magnetic head. The polyurethane resin having low hardness is used in combination with the rigid resin to improve the poor contact.
The polyurethane resin is inherently low in hardness, so that when a magnetic recording medium such as video tape is used under a severe condition such as that in a still mode in which the same surface of the magnetic recording layer is brought into contiunous contact with a rotating magnetic head, the surface of the recording layer is liable to be scratched by the magnetic head.
Particularly in the case of a video tape having a width of 8 mm for the 8 mm-type video system (i.e., 8 mm-type video tape) which has been paid much attention in recent days, reconding of a higher density should be done as compared with the conventional video tape, because the 8 mm type video tape has a narrower width than the conventional video tape. Accordingly, even if a slight scratch is produced, the magnetic recording layer is caused to show prominent decrease in the image quality, and therefore the magnetic recording layer of the 8 mm type video tape is required to have much higher running endurance than the conventional video tape.